"since you believe that it is OK to let 'fertile' animals roam freely and mate whenever they feel the need"
That is not exactly the correct context I am implying. Perhaps you may want to study the history of breeding dogs and cats. I feel it is wrong. Sure they are cute, because if you leave them to breed on their own, for example, the dogs will all look like wild dogs with pointy noses. Humans interfered with nature and began breeding them. I am against that and I am against taking their organs out. If people want dogs and cats, then they can figure out a way to not let them get pregnant and surgery is not the answer, in my opinion.